Amanda Howe, Joseph Capriotti, MD, and Aron Shapiro


Antiseptics are used for surgical sterilization, treatment of infection, prophylaxis and medication preservation. Endophthalmitis arising from cataract surgery is a rare but serious complication thought to derive largely from microflora in the ocular tear film, lids and adnexa gaining entry to the anterior chamber during surgery.1 Similarly, refractive surgery poses the risk of keratitis, with microflora entering the cornea. Surgeons therefore use antiseptics as a part of routine preoperative procedures to sterilize the ocular surface and surrounding area. Antiseptics are also used routinely in neonatal conjunctiva.2 Doctors prophylactically instill drops of silver nitrate, erythromycin or tetracycline bilaterally into neonates to prevent disease, per recommendations of the Centers for Disease Control and Prevention.3


Antiseptics and preservatives fall under the umbrella of biocides, which also includes disinfectants (agents used on nonliving surfaces). Antiseptics, which are bactericidal, are used to prevent sepsis through decreasing the bacterial load, while bacteriostatic preservatives are used to prevent bacterial growth. Some biocides, such as povidone-iodine, have crossover capabilities and have wide applications and high degrees of efficacy. There is a wide range of available antiseptics, with varied efficacies against multitudes of microbes. However, just as with antibiotics, resistance can be a concern, and it's important to preserve the ability of antiseptics to control and prevent ocular infections.

 


Background and Development

Discoveries of antiseptics and preservatives were initially linked to humanity's ambition for expansion and conquest. Early travel was inhibited by innocuous wounds developing into lethal infections as well as food and water contamination and spoilage. In about 450 BC, the Persians realized that copper and silver-lined containers maintained water's freshness. Boiling water before drinking also became common practice around this time, although heat sterilization was not widespread until after the discoveries of Louis Pasteur in the 18th century.4


Records from the 4th century indicate the use of mercury by Arab physicians as an antiseptic—until its toxic effects were realized. Throughout the centuries, people discovered the antiseptic properties of silver, copper and zinc. The bleaching powers of chlorine were recognized in the 1700s and soon it was used to prevent infection in wounds and as a gargle for infected sore throats. After it helped curb the cholera epidemic of the 19th century, chlorine was used to create an entire class of N-chloro compounds. Iodine and hydrogen peroxide became prevalent antiseptics in the 19th century, and both are still used today. The 20th century saw the development of quaternary ammonium compounds such as chlorhexidine, which is one of the most recent advances in antiseptic research.
4

 



The Array of Antiseptics

Molecular iodine has inherent antiseptic properties due to its electronegativity. In solvent-based systems, diatomic neutral (i.e., free) iodine has the ability to oxidize thiol moieties (-SH) with the rapid formation of disulfides (R-SS-R). Additionally, free iodine can undergo substitution for hydrogen on activated aromatic systems (including many naturally occurring amino acids) and mono- or di-iodination with certain olefins that are present in all unsaturated fatty acids. As the uncharged free iodine can easily pass through the cell walls of microorganisms, it's thought that all of these reactions contribute to the germicidal efficacy of iodine in living microorganisms.


Though molecular iodine is an effective antiseptic in aqueous or alcoholic solvents, its use was originally limited by poor solubility, dramatic chemical instability and severe irritation of mucous membranes. In the 1800s, the French doctor J.G.A. Lugol developed a solution of elemental iodine with iodine potassium salts and used it for the treatment of bronchocele and tuberculous skin lesions, but stability problems, skin staining, stinging in open wounds, allergies and mucosal toxicity hindered its use.
5


Today, modern medical formulations are compounded with polyvinylpyrrolidone. Povidone-iodine (PVP-I) is used in every medical arena, whenever the skin is to be ruptured. It was approved as a dermatological solution in the 1950s, and then as an ophthalmic solution in 1986. It's used prophylactically to kill and hinder the growth of bacteria prior to surgery, both on the skin and in the eye for ocular surgical procedures.1 In its 150 years of use, PVP-I has demonstrated potent bactericidal, fungicidal, virucidal, amoebicidal and sporicidal properties.


After penetrating the membranes of microorganisms, PVP-I reacts with key proteins and nucleotides through the mechanisms described above, inducing cell lysis, according to information provided by Internatinoal Specialty Products, an iodine maker. It's more effective against non lipid-enveloped viruses, likely due to affinity for the surface proteins on the lipid membrane.6 One interesting observation is that more dilute formulations of PVP-I demonstrate greater and more rapid killing efficacy than more concentrated ones, while also being less irritating to mucosal surfaces.7 To this end, the ophthalmic solution ranges from 1.25% to 5% while the dermatological solution ranges from 5% to 10%.


Recently, povidone-iodine 1.25% ophthalmic solution was compared to neomycin, polymyxin B and gramicidin ophthalmic solutions for the treatment of infectious conjunctivitis in a study (n=459) of children aged 7 months to 21 years in the Philippines. The most notable outcome of the study was the observation that the younger the patient, the more quickly the conjunctivitis resolved (p=0.13). Statistically significant differences were not observed between the various ophthalmic solutions, (p=0.133 to 0.824 for the four groups). This suggests that PVP-I is as effective as neomycin, polymyxin B and gramicidin in the treatment of bacterial conjunctivitis.
8




In a study (n=475) of neonates, povidone-iodine was assessed for its self-preservation effect, among other endpoints. The 2.5% solution demonstrated sufficient antimicrobial action against Aspergillus niger, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus at 7, 14, 21 and 28 days after incubation to merit it being called a self-preservative. Only 0.84 percent of neonates contracted S. epidermis conjunctivitis, 0.63 percent developed conjunctivitis related to S. aureus and 0.21 percent contracted P. aeruginosa conjunctivitis
.9


In addition to PVP-I, a battery of other antiseptics are in use. Chlorhexidine glucate (CHX), for example, has been used for more than 30 years against bacterial skin infections, open wounds and gingivitis. Commercially available chlorhexidine-based products include Peridex Oral Rinse and Hibistat Towlettes. Through extemporaneous compounding, chlorhexidine has also been investigated as a 0.02% drop for ocular and mucosal infections.10 Chlorhexidine, although pH-dependent and therefore of varying efficacy, is a broad-spectrum antiseptic, disinfectant and preservative. Bacterial uptake of chlorhexidine has been shown to be very rapid, with maximum bioavailability reached in less than 20 seconds. Chlorhexidine damages the cell membrane and then causes intracellular elements to leak through the resulting semi-permeable membrane. It also has a biphasic lethal effect: Once concentrations of chlorhexidine become high in the target cell, the cytoplasm begins to coagulate, reducing leakage and then inhibiting enzyme activity.
6


Efficacy of chlorhexidine may vary. In a small study (n=5) of patients infected with Acanthamoeba keratitis (AK), CHX was found to be effective at a concentration of only 0.006%.11 Symptoms decreased within a week, ulcers were healed in a mean of 19 days, and visual acuity improved by 80 percent in two to three weeks. Acanthamoeba keratitis did recur in one patient but was eradicated with persistent dosing of CHX.11 Another study found (n=25) that a 4% solution of PVP-I reduced conjunctival bacterial flora in a way similar to 0.05% CHX before cornea suture removal. Because the incidence of endophthalmitis is rare, this could not be used as an endpoint for comparison; instead the number of colony- forming units was measured. The mean percent reduction of CFUs by PVP-I was 91.2 percent vs. an 87.6 percent reduction by CHX (p= 0.68).
12


In a study regarding catheter preparation prior to insertion (n=119), PVP-I and CHX were compared individually and as a combination to determine the most effective method of establishing and maintaining antisepsis. Skin disinfection with a 10% PVP-I application resulted in microbial growth on 30.8 percent of the catheters, and disinfection of the catheter with a 0.05% solution of CHX resulted in growth on 24.4 percent of the devices. When the two methods, instrument and skin disinfection, were used in tandem only 4.7 percent of the catheters yielded microbial growth (p=0.006).13 Combination therapy appears to be promising, but research into creating antiseptic devices is also ongoing.

N-Chlorotaurine is a mild, well-tolerated, long-lived oxidant that mimics the oxidative burst of white blood cells when killing bacteria.14 NCT is an antiseptic and disinfectant that destroys intracellular proteins and is potentiated by low pH environments. It also possesses sporicidal and virucidal properties.6 Ammonium chloride (NH4Cl) has been shown to markedly enhance the activity of NCT against bacteria and fungi in vivo. NCT alone is barely able to penetrate the cornea but the addition of NH4Cl was shown to aid penetration.14


A 2007 study suggests that current Acanthamoeba keratitis therapy with CHX is difficult to handle logistically, as it requires hourly application in the beginning and, in some cases, the application needs to be sustained for months. Still, it's among the most effective treatments available. Since all known AK strains are susceptible to NCT,15 it may become a viable option in the future. NCT has proven virucidal, bactericidal and fungicidal properties as well as very good tolerability in a 1% solution.

 


Antisepsis Using Silver

Through hydrogen bonding, silver is able to bind to the key functional groups of microorganisms and inhibit their enzymes. It can impede cell division and damage the cell envelope as well.6 Silver coating of medical devices is believed to prevent device-related infection, but the efficacy of such a coating is not yet proven. Silver has known antimicrobial properties combined with exceptionally low human toxicity, making it a promising area of research. Silver-coated catheters, for example, could reduce infection in catheterized patients by half.16 An example of silver's preservative efficacy can be found in over-the-counter artificial tears. Visine Pure Tears, housed in a bottle with a silver-threaded coil at the tip to reduce contamination, is one such preservative-free artificial tear. Further research in this area would be compelling.


Used since the 1880s against neonatal conjunctivitis, 1% silver nitrate drops have a long history and are still used very frequently in developing nations for this indication. Silver ions bind to bacterial DNA and inhibit phosphate uptake and cellular oxidation processes,16 effectively killing the bacteria.


The efficacy of 1% silver nitrate drops as a prophylactic was studied in newborns (n=630). After two months of observation, 22 percent of babies with no prophylaxis had contracted conjunctivitis compared to only 14 percent of babies who had been given silver nitrate drops; they  also had a 39 percent lower rate of conjunctivitis (p=0.038).17 Silver nitrate's ability to reduce bacterial growth will probably lead to opportunities in other therapeutic areas.

 


Antiseptic Resistance

Antiseptics employ a battery of mechanisms to induce cell lysis, including leakage of intracellular constituents, destruction of membrane integrity, inhibition of enzymes and disruption of biosynthetic processes.6 Microorganisms, however, have developed modes of resistance to these processes. They can develop waxy cell walls to prevent biocide entry, use efflux pumps to expel biocides already inside or have intrinsic mechanisms of resistance.6 While no bacteria are known to be resistant to PVP-I, mycobacteria are highly resistant to chlorhexidine. Furthermore, chlorhexidine isn't sporicidal and its efficacy varies as a virucide.6 Sporadic resistance to silver has been documented since the late 1990s, but has remained rare.6 A few organisms, Pseudomonas stutzeri, Enterobacteriaceae, and several species of Citrobacter have shown plasmid-mediated resistance, but the mechanism is unknown.6


There is a wide range of antiseptics from which to choose. The definition of an antiseptic implies that it's viable against a spectrum of microbes, but no one antiseptic can combat them all. Furthermore, many clinical trials have resulted in only nuanced differences in efficacy. No large-scale, prospective, randomized, head-to-head studies have been completed to demonstrate statistical significance of one over the others. Although some microorganisms have shown an aptitude in resisting them, the wide variety of antiseptics available preserves their importance in the health-care field. 

 

Dr. Abelson, an associate clinical professor of ophthalmology at Harvard Medical School and senior clinical scientist at Schepens Eye Research Institute, consults in ophthalmic pharmaceuticals. Dr. Capriotti is an ophthalmologist at Foresight Biotherapeutics in New York City, and an Adjunct Research Scientist in  Columbia University's Department of Chemistry. Mr. Shapiro is director of anti-infectives and anti-inflammatories and Ms. Howe is a medical writer at ORA Clinical Research and Development in Andover, Mass.

 

1. Ciulla TA, Starr MB, Masket S. Bacterial endophthalmitis prophylaxis for cataract surgery: An evidence-based update. Ophthalmology 2002;109:13-24.

2. Isenberg SJ, Apt L, Wood M. A controlled trial of povidone iodine as prophylaxis against ophthalmia neonatorum. N Engl J Med 1995;332:9:562-566.

3. Workowski KA, Levine WC. Sexually transmitted diseases treatment guidelines 2002. CDC Recommendations and Reports 2002;51:RR06:1-80.

4. Hugo WB. A brief history of heat and chemical preservation and disinfection. J Appl Bacteriol 1991;71:1:9-18.

5. Gottardi W. Iodine and iodine compounds. In: Block SS, ed. Disinfection, Sterilization, and Preservation, Fifth Edition. Lippincott Williams & Wilkins, 2000:159-204.

6. McDonnell G, Russell AD. Antiseptics and disinfectants: Activity, action and resistance. Clin Microbiol Rev 1999;12:1:147-179.

7. Berkelman RL, Holland BW, Anderson RL. Increased bactericidal activity of dilute preparations of povidone-iodine solutions. J Clin Microbiol 1982;15:2:635-639.

8. Isenberg SJ, Apt L, Valenton M, Signore MD, Cubillan L, Labrador MA, Chan P, Bergman NG. A controlled trial of povidone-iodine to treat infectious conjunctivitis in children. Amer J Ophthalmol 2002;134:5:681-688.

9. Najafi RB, Samani SM, Pishva N, Moheimani F. Formulation and clinical evaluation of povidone-iodine ophthalmic drop. Iranian J Pharm Res 2003;2:157-160.

10. Kairuz T, Chhim S, Hasan F, Kumar K, Lal A, Patel R, Singh R, Dogra M, Garg S. Extemporaneous compounding in a sample of New Zealand hospitals: A retrospective survey. NZ Med J 2007;120:1250:1-9.

11. Kosrirukvongs P, Wanachiwanawin D, Visvesvara GS. Treatment of acanthamoeba keratitis with chlorhexidine. Ophthalmology 1999;106:4:799-802.

12. Barkana Y, Almer A, Segal O, Lazarovitch Z, Avni I, Zadok D. Reduction of conjunctival bacterial flora by povidone-iodine, ofloxacin and chlorhexidine in an outpatient setting. Acta opthalmologica Scandinavica 2005;83:3:360-363.

13. Langgartner J, Lind HJ, Lehn N, Reng M, Scholmerich J, Gluck T. Combined skin disinfection with chlorhexidine/propanol and aqueous povidone-iodine reduces bacterial colonisation of central venous catheters. Intensive Care Med 2004;30:6:1081-1088.

14. Fürnkranz U, Nagl M, Gottardi W, Kohsler M, Aspock H, Walochnik J. Cytotoxic activity of N-chlorotaurine on acanthamoeba spp. Antimicrob Agents and Chemother 2007;52:2:470-476.

15. Teuchner B, Schmid E, Ulmer H, Gottardi W, Nagl M. Tolerability and efficacy of N-chlorotaurine in epidemic keratoconjunctivitis – a double-blind, randomized, phase-2 clinical trial. J Ocular Pharmacol Thera 2005;21:2:157-164.

16. Schierholz JM. Lucas LJ, Rump A, Pulverer G. Efficacy of silver-coated medical devices. J Hosp Infect 1998;40:4:257-262.

17. Bell TA, Grayston JT, Krohn MA, Kronmal RA. Randomized trial of silver nitrate, erythromycin, and no eye prophylaxis for the prevention of conjunctivitis among newborns not at risk for gonococcal ophthalmitis. Pediatrics 1993;92:6:755-760.